In Vitro Screening of Chemopreventive Agents Using Primary Human Epidermal Cells (Workstatement # 51) Human foreskin tissue samples are obtained during routine surgical procedures under sterile conditions. An initial cytotoxicity assay is used to assess the relative toxicity of each chemopreventive test agent and to permit the selection of approximate concentration ranges for the inhibition assay. Primary cultures of human epithelial cells are exposed to propane sultone for three days each week during the assay. Medium which is changed twice weekly contains chemopreventive test agent throughout the exposure period. Five concentrations at half-log dilutions of the test agent are being assayed for each agent. The positive control cultures are treated with 30 ng/ml retinoic acid using the same regimen as the chemopreventive agent. The cultures are subcultured routinely and subcultured four times during the chemical treatment phase. Fourth passage cells are plated into culture medium containing added calcium chloride at 17.5 mug/ml. After a 5-7 day incubation period the cultures are stained and scored for relative growth. Triplicate cultures per condition are evaluated. The data are corrected for control growth and differentiation and analyzed for inhibition of growth and induction of differentiation. Fourth passage cells are plated for the induction of differentiation by the test agent at five doses. Sixteen agents are being evaluated.